如何使 VB.NET 函数的参数作为泛型类型？
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How to make Parameters of VB.NET function as Generic type?
提问by N.T.C
I have a VB.NET function as below, the parameter 'x' that is passed to the function is of Type 'Single'. However, I want to write the function so that it can accept any numeric type such as 'Single', 'Double' and 'Integer'. I know one way of doing that is to write 3 functions with the same names, but it would be so tedious. Can anyone suggest any idea? Thank you.
我有一个 VB.NET 函数，如下所示，传递给该函数的参数“x”的类型为“Single”。但是，我想编写函数以便它可以接受任何数字类型，例如“单”、“双”和“整数”。我知道这样做的一种方法是编写 3 个具有相同名称的函数，但这会很乏味。任何人都可以提出任何想法吗？谢谢你。
Public Function Square(x As Single) As Single
Return x * x
End Function
回答by Shell
try following method
试试下面的方法
Public Function Square(Of T)(ByVal x As Object) As T
Dim b As Object = Val(x) * Val(x)
Return CType(b, T)
End Function
You can use above function like this
您可以像这样使用上述功能
Dim p As Integer = Square(Of Integer)(10)
Dim d As Double = Square(Of Double)(1.5)
回答by Bj?rn-Roger Kringsj?
You can constrain the generic type by IConvertibleand Structure. The following data types implements the IConvertible interface:
您可以通过IConvertible和来约束泛型类型Structure。以下数据类型实现了 IConvertible 接口：
- System.Boolean
- System.Byte
- System.Char
- System.DateTime
- System.DBNull
- System.Decimal
- System.Double
- System.Enum
- System.Int16
- System.Int32
- System.Int64
- System.SByte
- System.Single
- System.String
- System.UInt16
- System.UInt32
- System.UInt64
- 系统布尔值
- 系统字节
- 系统字符
- 系统日期时间
- System.DBNull
- 系统.十进制
- 双系统
- 系统枚举
- System.Int16
- System.Int32
- System.Int64
- 系统字节
- 系统单机
- 系统字符串
- System.UInt16
- System.UInt32
- 系统.UInt64
Here's a rewrite of the code found in the link provided by SLaks:
这是对 SLaks 提供的链接中的代码的重写：
Public Function Square(Of T As {IConvertible, Structure})(x As T) As T
'TODO: If (GetType(T) Is GetType(Date)) Then Throw New InvalidOperationException()
Dim left As ParameterExpression = Expression.Parameter(GetType(T), "x")
Dim right As ParameterExpression = Expression.Parameter(GetType(T), "x")
Dim body As BinaryExpression = Expression.Multiply(left, right)
Dim method As Func(Of T, T, T) = Expression.Lambda(Of Func(Of T, T, T))(body, left, right).Compile()
Return method(x, x)
End Function
Reference: https://jonskeet.uk/csharp/miscutil/usage/genericoperators.html
参考：https: //jonskeet.uk/csharp/miscutil/usage/genericoperators.html
回答by Tripweed
The code allows any value to posted via Arg but only numeric values will be processed. The returned value must be double because Val returns double only.
该代码允许通过 Arg 发布任何值，但只会处理数值。返回值必须是双精度值，因为 Val 只返回双精度值。
The Of T allows for generic object types to be presented.
Of T 允许呈现通用对象类型。
Private Function sqr(Of T)(Arg As T) As Double
If IsNumeric(Arg) Then
Return Val(Arg) * Val(Arg)
Else
Return 0
End If
End Function
